Recently, a displacement element, which makes it possible to adjust the optical path length and the position in an order of submicron, is required, for example, in the fields of optics, magnetic recording, and precision machining. Development is advanced for the displacement element based on the use of the displacement brought about by the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric material).
As shown in FIG. 53, for example, those hitherto disclosed as such a displacement element include a piezoelectric actuator comprising a fixation section 404, a movable section 406, and a beam section 408 for supporting them which are formed in an integrated manner with a hole 402 provided through a plate-shaped member 400 composed of a piezoelectric/electrostrictive material and with an electrode layer 410 provided on the beam section 408 (see, for example, Japanese Laid-Open Patent Publication No. 10-136665).
The piezoelectric actuator is operated such that when a voltage is applied to the electrode layer 410, the beam section 408 makes expansion and contraction in a direction along a line obtained by connecting the fixation section 404 and the movable section 406 in accordance with the inverse piezoelectric effect or the electrostrictive effect. Therefore, the movable section 406 can perform circular arc-shaped displacement or rotational displacement in the plane of the plate-shaped member 400.
On the other hand, Japanese Laid-Open Patent Publication No. 63-64640 discloses a technique in relation to an actuator based on the use of a bimorph. In this technique, electrodes for the bimorph are provided in a divided manner. The actuator is driven in accordance with the selection of the divided electrodes, and thus the highly accurate positioning is performed at a high speed. This document (especially in FIG. 4) discloses a structure in which, for example, two bimorphs are used in an opposed manner.
However, the piezoelectric actuator described above involves such a problem that the amount of operation of the movable section 406 is small, because the displacement in the direction of expansion and contraction of the piezoelectric/electrostrictive material (i.e., in the in-plane direction of the plate-shaped member 400) is transmitted to the movable section 406 as it is.
All of the parts of the piezoelectric actuator are made of the piezoelectric/electrostrictive material which is a fragile material having a relatively heavy weight. Therefore, the following problems arise. That is, the mechanical strength is low, and the piezoelectric actuator is inferior in handling performance, shock resistance, and moisture resistance. Further, the piezoelectric actuator itself is heavy, and its operation tends to be affected by harmful vibrations (for example, residual vibration and noise vibration during high speed operation).
In order to solve the problems described above, it has been suggested that the hole 402 is filled with a filler material having flexibility. However, it is clear that the amount of displacement, which is brought about by the inverse piezoelectric effect or the electrostrictive effect, is decreased even when the filler material is merely used.